1. Field of the Invention
This invention relates to an image pickup apparatus and more particularly to an image pickup apparatus arranged to process digital signals.
2. Description of the Related Art
A single-plate color image pickup method, i.e., a method of picking up a color image by means of a single solid-state image sensor which has minute color filters arranged on its image pickup plane has been well known.
According to this method, a luminance signal is first formed by removing a carrier component from a color signal outputted from the image sensor. A chrominance signal is formed by carrying out a synchronous detection process on the carrier component. The chrominance and luminance signals are processed separately from each other before a color image pickup signal is composed from them.
Reduction in size and increase in recording density of the image pickup apparatuses of the kind using the single-plate color image pickup method have progressed with the recent advancement of electronic technology. The advancement of semiconductor technology in particular has come to permit high speed analog-to-digital (hereinafter referred to as A/D) and digital-to-analog (hereinafter referred to as D/A) converters to be practical.
As a result, there have been proposed methods of converting the image pickup signal outputted from the image sensor which is a CCD or the like into a digital signal and carrying out a digital signal processing action on the digital signal using these A/D and D/A converters. According to these methods, the image pickup signal is A/D-converted and signal processing actions such as filtering, synchronous detection, gamma correction, matrixing, etc., are carried out. After these processes, the image pickup signal is outputted by D/A-converting it.
The conventional image pickup apparatus using the above-stated digital signal processing method has been arranged to carry out digital processes by using such circuits that had been adapted for analog processes as they are. Therefore, the conventional arrangement has caused the apparatus to have a large electric current consumption and a large circuitry, which is too large to be covered by a single integrated circuit and prevents reduction in cost. Further, the conventional image pickup apparatus has had its digital system not arranged apposite to a digital signal processing operation. As a result, there have occurred a spurious contour, deterioration of frequency characteristic, etc., due to a place cancelling phenomenon peculiar to digital systems.